1. Field of the Invention
This invention relates to a control valve, and particularly to a plug type control valve for controlling the flow of fluids or fluidized materials through a conduit, such as the powered catalyst transfer lines and flue gas vent stacks employed in fluid catalytic cracking systems and in fluid catalytic hydroforming systems in the petroleum refining art; and to a sealing assembly for providing a seal between the stem tube and guide tube of a plug valve; and to a plug valve with such a sealing assembly.
2. Description of the Prior Art
In the chemical and petroleum industries fluid catalytic methods are employed in which finely divided catalyst particles are maintained suspended in a gas in the so-called "fluid state" under reaction conditions. Particles in the fluid state act in many ways like a liquid and undergo hindered settling. Thus, they may be conveyed from one vessel to another through a conduit, they develop a pressure head, etc.
Large units can operate continuously on-stream for extended periods of time under closely controlled conditions by employing fluid catalytic procedures. Catalysts in such units in processes where deposition of undesirable coke or other contaminant is encountered during the reaction state may be maintained at a predetermined level by continuously circulating the catalyst from the fluid reactor to a regenerator, where such coke or contaminant is removed, as by oxidative combustion. Fluid units of large capacity, such as a through-put of sixty thousand barrels or more of charge per day, are intended to operate on-stream for periods of as long as a year or more without being shut down.
Various applications involve high temperature operations in the chemical processing and petroleum refining arts, including use in a converter, such as a fluid catalytic cracking unit or a fluid catalytic hydroforming unit of conventional design, having superimposed contact chambers in which the catalyst is maintained in a state of phase separation comprising an upper diffuse phase and a lower dense pseudo-liquid phase, the catalyst being withdrawn from the lower dense phase of the upper chamber through a vertical internal standpipe and discharged at a low point within the dense phase of the lower chamber and, after suitable treatment in the lower chamber, being returned upwardly through an internal vertical carrier line to the dense phase of the upper chamber.
By passing catalyst by gravity flow from the upper chamber to the lower chamber through a standpipe and passing the catalyst from the lower chamber to the upper chamber through a carrier line by injection thereinto a stream of the gas to be contacted in the upper chamber, a continuous flow of the mixture upwardly through the carrier line is produced. In those cases where a regeneration zone is superimposed upon a conversion zone, the gas introduced into the carrier line is ordinarily air or other oxygen-containing gas. In those cases where the conversion zone is superimposed upon the regeneration zone the gas introduced into the carrier line is a stream of vaporous hydrocarbons.
Flow control of catalyst from the standpipe into the dense phase of the lower chamber and from the latter into the carrier line for conveyance into the upper chamber is obtained by the use of plug valves engageable with the lower ends of the transfer lines and having elongated valve stems extending through the vessel wall controlled in their longitudinal movement by external mechanical or manual operating means. These plug valves are used in oil refineries in controlling the flow of catalyst into a reaction chamber which is subject to temperature extremes, for example, in the range of 1500.degree. F., as well as in other industrial applications wherein the valves are subject to oppositely directed displacements due to thermal expansion and spring forces.
Plug valves (such as Kellogg Orthoflow Valve, U.S. Pat. No. 2,850,364) are used to control the flow of catalyst to introduce a lift medium such as oil feed stock or lift air into a riser line. One problem occurring with the hollow tube plug valve providing a lift medium through the center hollow section is that the lift medium pressure at the inlet of the valve cannot be maintained at a high enough level to overcome the bottom regenerator pressure. If the regenerator pressure is greater than the lift air pressure, catalyst from the regenerator can block the valve's guide liners and cause the valve to stick. Another problem with prior art valves occurs when the pressure of the lift medium is greater than the regenerator pressure, permitting the lift medium to go between the valve's guide liners causing the valve to stick.
There has been a long-felt need to overcome the problems associated with the prior art plug valves. The present invention addresses and satisfies this long-felt need.
Applicant believes U.S. Pat. Nos. 2,668,755 and 4,518,146 and the two publications from Hydrocarban Processing are pertinent to the present invention, but fail to teach either alone or in combination the unique, novel and unobvious combinations and apparatuses of the present invention.